The present invention relates to a display method and an apparatus used in a numerical control apparatus in a case where the cross sectional shape of a material which is a rotating body is painted out and displayed.
For example, when machining tests of machining programs for lathes are carried out on a CRT screen of a numerical control apparatus, the cross sectional shape (hereinafter referred to as a "material shape") of the material must be displayed on the CRT screen. On that occasion, to make the material shape clear, the material shape is painted out.
FIG. 1 is a flowchart for explaining a paint-out shape display method in a numerical control apparatus of the prior art. For example, when a material shape, as shown in FIG. 2C, is displayed on a CRT screen, it is shown in the X-Z coordinates with the Z-axis as the center axis. As shown in FIG. 2A, shape elements a to j of the upper half only with respect to the center axis are input as the material shape element sequence (Step S1). A determination is then made as to whether or not an inner circumference exists in the material (Step S2). Since an inner circumference exists in this case, the material shape is separated into an outer circumference (solid line portion) and an inner circumference (dashed line) as shown in FIG. 2B (Step S3). Outer circumference basic shapes OF1 and OF2 are generated after the start points P.sub.b and P.sub.c and the end points P.sub.c and P.sub.d of the shape elements b, c of the outer circumference and their symmetrical points P.sub.b ', P.sub.c ' and P.sub.c ' and P.sub.d ' on the Z-axis are respectively connected to each other with striaght lines and those shapes are then divided by these lines (Step S4). The inside of the generated outer circumference basic shapes OF1 and OF2 are painted out and displayed on a CRT screen (Step S5). Similarly, inner circumference basic shapes IF1, IF2, IF3 and IF4 are generated after start points P.sub.e, P.sub.f, P.sub.g, and P.sub.h and end points P.sub.f, P.sub.g, P.sub.h, and P.sub.i of shape elements e,f,g, and h of the inner circumference and their symmetrical points P.sub.e ', P.sub.f ', P.sub.g ', and P.sub.h ' and P.sub.f ', P.sub.g ', P.sub.h ', and P.sub.i ' are respectively connected to each other with straight lines and the shapes are divided by these lines (Step S6). A material shape as shown in FIG. 2C can be displayed on the CRT after the inner circumference basic shapes generated in an outer circumference basic displayed on the CRT are combined and the inside of the inner circumference basic shape is erased (Step S7), thereby completing the whole process. On the other hand, when an inner circumference portion does not exist in the material at the above Step S2, it is assumed to be only shape elements of the outer circumference portion and the outer circumference basic shape is generated by the same process as that of the Step S4. The inside of the generated outer circumference basic shape is painted out and displayed on the CRT (Step S9), thus completing the whole process.
In the above-mentioned paint-out shape display method of a conventional numerical control apparatus, in a case of material shape seen in casting and so forth, there has been a problem in that the recess of the end surface composed of shape elements D, E, F, and G and the inner circumference portion composed of shape elements I, J, and K overlap and cannot properly be displayed on the CRT.